Nowadays wafer manufacture techniques are developed toward the trends of large wafer size, small chip size, and complicated process. For example, the geometry dimension shrinks from 90 nm to 7 nm, 5 nm, 3 nm, and below. The immersion lithography technique is introduced in the design stage of about 45 nm, the high-k metal gate structure is introduced in the design stage of about 28 nm, and the finFET structure is introduced in the design stage of about 14 nm. Before delivering manufactured wafers to the IC design house, it is very important to perform inspection processes on the manufactured wafers to detect potential defects that are likely to negatively affect the yield.
In the manufacturing stage, the fabrication plant generally increases the sensitivity of inspection apparatuses to avoid ignoring the potential defects that are likely to affect the yield. This also results in an increase of quantity of detected defects accompanied with dummy and nuisance defects. Subsequently, the fabrication plant further utilizes scanning electron microscopy (SEM) apparatuses to analyze and sample the detected defects, so as to find out the root cause of the problem and quickly solve the problem. However, the SEM apparatuses in the fabrication plant have a limited velocity per hour in processing defects. The conventional method is that the inspection apparatus randomly samples small quantities of defects (e.g., 100 defect counts) from the scanned defects (e.g., several thousand to several ten thousand defect counts) of each SEM apparatus for analysis. In this situation, the inspection apparatus has a sample rate within several percentage points, or even less than one percentage point. The potential defects that are likely to negatively affect the yield are unlikely to be found, especially in the circumstance that various apparatuses and processes work together.
Therefore, there is an urgent need for a quick and efficient method which can monitor systematic defects and random defects during the manufacturing process, so that the mass production time and the profit would not be negatively affected.